Homocystinuria is a disorder that results in marked elevation of homocyst(e)ine in the plasma. Several inborn errors of metabolism, including cystathionine -synthase deficiencies, abnormalities in 5 methyl tetrahydrofolate-dependent conversion reaction and several conditions leading to Vitamin B12 or Vitamin B6 deficiencies, increase homocyst(e)ine levels. The clinical manifestations of homocystinuria include ocular, skeletal, central nervous system and vascular complications. Moderately elevated plasma levels of homocyst(e)ine have been found in patients with peripheral vascular disease. Furthermore, the heterozygous state for homocystinuria has been found to be frequent in patients with cerebral arterial disease. In addition, moderately elevated homocyst(e)ine levels may be a risk factor for the development of coronary artery disease. Transesophageal echocardiography is an acceptable technique for visualizing and quantitating the extent of atherosclerosis in the thoracic aorta. In association with Dr. Itzhak Kronzon, we measured homocyst(e)ine plasma levels in patients referred for clinically indicated transesophageal echocardiography. Results demonstrated a significant positive association between homocyst(e)ine and the extent of aortic atherosclerosis.